Abstracts

Rationale: Oxcarbazepine and carbamazepine, anticonvulsants used to manage partial seizures, are a known cause of hyponatremia largely due to increased tubular sensitivity to ADH. Common ways of addressing this include fluid restriction and enteral sodium chloride (NaCl) supplementation. These solutions however increase the risk of developing nephrolithiasis or nephrocalcinosis in medically complex patients with intractable epilepsy who are largely sedentary. As an alternative, we sought to determine if urea, by osmotic increase in free water excretion, was effective in safely correcting hyponatremia. We present a series of 4 patients whose hyponatremia resolved with the introduction of urea in place of NaCl. Methods: The 4 patients, ranging in age from 6 to 17 years, were found to have hyponatremia with a nadir between 122 and 131(Figure 1 shows median values) after starting oxcarbazepine. Each patient was started on NaCl (from 1-4mEq/kg/day) with some doing fluid restriction; sodium levels  nevertheless remained in the low 130s.  The patients were  then started on enteral urea (g-tube, j-tube or orally) at 15g (250 mosm) to 30g (500 mosm) daily . Results: Serum sodium levels normalized within 1-2 weeks of starting urea (see Figure 1). Three of the four patients have been successfully weaned off NaCl supplementation with plans to wean the fourth as well. Conclusions: Our results show that urea is effective in treating oxcarbazepine-induced hyponatremia. It works to increase urine osmolarity, increasing the excretion of electrolyte-free water. It has been suggested in an animal model to also have neuroprotective effects minimizing risk of osmotic demyelination resulting from rapid correction of chronic hyponatremia. Urea does not potentiate the formation of stones and as it allows for an electrolyte free-water diuresis it may enable less fluid restriction, help reduce urinary solute concentration and increase urine flow, thereby contributing to stone prevention. It is easy to administer, is not nephrotoxic and can be reliably obtained from retail pharmacies. Given these results, urea may also be a useful alternative for symptomatic hyponatremia in place of hypertonic saline or vaptans. Funding: No funding was received.